I've been in your shoes bro..I tried to remain calm and quiet in the face of an A by my W. Had sex, acted normal..all that crap just to try and save the marriage.
You know what I got?
I got a beat up self-esteem for allowing my self to get used. I got treated to more OMs. I got the bomb dropped on me anyway.
If you have proof the A is going on; you need to confront to save yourself. It will only damage you emotionally and mentally in the end if you don't.